Traditionally, it has been desirable to provide dressings for wounds such as those derived from ulcers, gangrene, burns, surgery, and the like, including infected wounds, which are sterilizable, air permeable, nontoxic, adherable to the wound area without bonding to the scab of the wound, and stable in storage. In addition, a high degree of absorbability for exudate, bacteria, infectious materials and the like is important as is wound cleaning, infection fighting and granulation and/or epithelization capability.
Conventional wound dressings of gauze or other fabric of natural or synthetic fibers, particularly regenerated cellulose, do not meet these requirements since they bond to the wound or the scab of the wound which is often torn off or dislodged during changing of the dressing with the result that the wound becomes irritated or inflamed and the healing process is interrupted and prolonged. In addition, the absorbability of such dressings is limited so that bacteria are not absorbed out of the wound, necessitating the application of bacteriocides such as antibiotics or sulfonamides.
To overcome these disadvantages, wound dressings which have non-adhering, flexible, perforated plastic films of various synthetic materials or metal foils on the wound side of the dressing have been offered on the market. While such dressings do not bond to the wound and permit wound exudate to permeate through the perforations to be absorbed by an absorbent layer beyond the film, the absorbability of the dressing is not increased. Consequently, wound exudate remains in the wound area, blocks the openings in the film, and creates an excellent medium for bacterial growth.
To increase absorbability, dressings have been prepared from natural or synthetic materials which are water insoluble but which swell when exposed to water. See for example U.S. Pat. No. 4,287,177 granted September 1981 to Nakashima et al. for "Wound Covering Material." Substrates prepared from starting material ranging from natural products such as chitin and chitosan, collagen, cellulose, cotton, silk, and the like (U.S. Pat. Nos. 4,035,483, 4,604,384 and 4,651,725 contain illustrative examples), to synthetic materials derived from various combinations of monomers have been proposed for this purpose. See U.S. Pat. No. 4,287,177, supra.
Most conventional wound dressings made of fabrics or fibrous materials are fabricated in the form of pads or sheets and, are generally flat in shape. Accordingly, they have little or no ability to conform to wound contours, much less penetrate into the interstices of a wound. An attempt to utilize a conventional dressing as a means of delivering salt to the wound has been made by Nordquist et al. U.S. Pat. No. 4,608,044 "Compress for Treatment of Wounds" granted Aug. 26, 1986. This approach, while effective in delivering small amounts of salt to the wound bed, does not overcome the disadvantages associated with conventional dressings (i.e., sticking to dried-out portions of the wound bed, inability to conform to small crevices and get into tunnels in the wound and possible severe foreign-body response due to entrapment in the healing wound).
While particulate matter such as powders are capable of conforming to uneven or fissured wound surfaces, their use is comparatively rare. For example, micropearls of cross-linked polysaccharide and polysaccharide derivatives, particularly dextran, can be applied directly to a wound. See, for example U.S. Pat. No. 4,554,156 granted Nov. 19, 1985 to Fischer et al. for "Wound Treating Agent." Spherical regenerated cellulose particles can also be used and both materials provide a high degree of absorbance for wound secretions. Nevertheless, the dextran materials, which swell on absorption of water or watery materials, are disadvantageous since the swelled spheres form a gel layer which reduces air permeability to the wound. While regenerated cellulose has a macroporous structure that can absorb water without swelling, the porosity of these materials is such that they absorb non-aqueous mediums such as organic solvents, which can have unfavorable effects.
It has recently been proposed to spread sodium polyacrylate powder as a dressing over a skin burn area and wetting the powder by spraying with water until the powder becomes moist. U.S. Pat. No. 4,732,755 granted Mar. 22, 1988 to Luis Grana for "Skin Burn Treatment." The outer moistened surface of the wetted powder layer is said to dry to provide a "parchment like" surface.
It has been found, however, that the best environment for wound healing is a moist or wet environment. See U.S. Pat. No. 4,671,267, granted Jun. 9, 1987 to Stout. Gels containing various components described as beneficial for wound treatment such as silver or zinc salts, antibiotics, antibacterial agents and the like have been proposed heretofore, principally in the form of thin films, otherwise called hydrogels. See for example, U.S. Pat. No. 4,587,284 granted May 6, 1986 to Luissi, et al. Earlier hydrogel patents include U.S. Pat. Nos. 4,584,188, 4,524,064 and 4,393,048. Such films do not conform to the interstices of a wound and provide no real debriding effect, particularly in the face of eschar which can mask infection and suppuration.
Other gels containing various components described as beneficial for the treatment of wounds in the form of jelly rather than a thin film have also been suggested. (U.S. Pat. No. 4,604,384, Smith, et al.) While some gels in this form can ooze into the interstices of a wound, they are equally likely to ooze back out. Increasing the viscosity of such gels does not significantly increase wound residence time since the tendency of a gel to flow away from or out of a wound in response to movement and/or gravity is not significantly reduced merely by an increase in its viscosity. Further, an increase in viscosity can only be achieved by adding to the already large quantities of gelling agent present in the composition, often exceeding 20-40% of its weight. Such agents, usually physiologically incompatible with the wound tissue, are often antithetical to the healing process. Moreover, such foreign materials can conceivably become incorporated in wound tissue as granulation and epithelialization occurs.
In addition to the risks involved in the application to a wound of physiologically incompatible gelling agents at extremely high concentrations, are the risks arising with the introduction of medication directly into exposed, severely traumatized tissue using such gels. Aside from allergic or hypersensitive reactions and the possible toxicity of many of these medications is the fact that they generally do not occur naturally in the body and, hence, can trigger rejection rather than healing mechanisms in wound tissue.